Various types of electrochemical sensors are known utilizing an ion conductive solid electrolyte. Most of those sensors operate only at an elevated temperature, for example above 400.degree. C., since the ion conductivity of the solid ion conductive elements is insufficient at a lower temperature. When used as an exhaust gas sensor in combination with internal combustion engines of the automotive type, even higher operating temperatures may be required to prevent impairment of operation of the sensor by lead contained in the exhaust gases. The output signal of the sensor is dependent on the temperature of the solid electrolyte. It has already been proposed to provide heating elements in combination with the sensors in order to reduce the response time of such sensors when exposed to cold gases and to obtain an output signal which can be readily analyzed and, further, to improve the lifetime of the sensor in the presence of exhaust gases from internal combustion engines which contain lead. Additionally, the accuracy of measurement is improved when the temperature of the element is high. It is thus desirable to supply heating elements to the sensors. The use of heating elements with such sensors is also indicated if the sensor is placed in positions in the exhaust system from internal combustion engines where the exhaust gases are already substantially cooled.
The sensor structure, which forms the basis of the structure of the present invention, is well known. Generally, the structure has been described, for example in U.S. Pat. No. 3,597,345. This type of sensor has a solid electrolyte tube which is closed at one end. A resistance heating element is provided, surrounding the closed tube with some distance. The resistance heater is a tubular element, positioned at the external or outer side of a tubular carrier body therefor. Such a sensor-heating element combination requires a specific and special type of heat insulation; the heating efficiency of the heating element is comparatively poor. The structure is expensive to make and thus is not suitable for mass production for automotive use and, further, difficulties arise with mounting of the various components in such a manner that they can withstand shocks and vibrations encountered in automotive applications.